Grace m908 User Manual
m908 Preliminary User Manual, Rev. 04
m908 multi channel monitor controller
PRELIMINARY
Entries marked ** are still to be defined.
Owner's Manual – Revision 01 / Feb 2019
RCU Firmware version: 0.01
ACU Firmware version: 0.01*
Grace Design, Lyons, CO / 1.303.823.8100
www.gracedesign.com / info@gracedesign.com
Page 1 of 108 Table Of Contents
Table of Contents
m908 Preliminary User Manual, Rev. 04
1 Welcome...................................................................4
2 Important Safety Information...................................4
2.1 General...................................................................4
2.2 Safety Marking Symbols.......................................4
2.3 Service Information...............................................4
2.4 California Proposition 65 Warning........................5
3 Overview And Features............................................5
3.1 Features..................................................................5
3.2 ACU Description...................................................6
3.3 ACU Front Panel Connections and Controls........8
3.4 ACU Rear Panel Connections...............................8
3.5 RCU Description.................................................11
3.6 RCU Front Panel Controls...................................11
3.7 RCU Rear Panel Connections.............................13
3.8 RCU Tilting Base................................................13
3.9 PSU Description..................................................14
3.10 PSU Front Panel Controls and Indicators.........14
3.11 PSU Rear Panel Connections............................14
4 Installation..............................................................15
4.1 Unboxing your m908...........................................15
4.1.1 Open and inspect your box.........................15
4.1.2 Your box will contain..................................15
4.1.3 REGISTER YOUR UNIT...........................16
4.2 Connecting the m908...........................................16
4.2.1 Power Connections.....................................16
4.2.2 Audio Connections......................................16
4.2.3 Optional ADC Module Connections...........17
4.2.4 Clock and Control Connections..................17
4.2.5 Thermal Management.................................18
5 Operation................................................................19
5.1 Manual conventions.............................................19
5.2 Home Screen........................................................20
5.2.1 1 Input Selection.........................................20
5.2.2 2 Control Room Speakers Layout Icons.....20
5.2.3 3 Control Room Speaker Output................21
5.2.4 4 Control Room Monitor Level..................21
5.2.5 5 Headphone Crossfeed..............................21
5.2.6 6 Headphone Monitor Level.......................21
5.2.7 7 SPL Meter................................................21
5.2.8 8 Clock Source and Status..........................22
5.2.9 9 System Sample Rate.................................22
5.3 INPUT SELECT..................................................22
5.3.1 Input Summing Mode.................................23
5.4 DIM......................................................................23
5.5 X-FEED...............................................................23
5.6 MONO / (L-R).....................................................25
5.7 MON>CUE..........................................................25
5.8 MUTE..................................................................26
5.9 CR1, CR2, CR3...................................................26
5.10 BASS MANAGEMENT...................................26
5.11 ROOM CORRECTION.....................................27
5.12 TALKBACK......................................................28
5.13 SOLO/MUTE....................................................31
5.14 VOLUME (push for phones).............................32
5.15 A B C User Switches.........................................33
5.16 Monitor Snapshots.............................................33
5.17 Meter Outputs....................................................34
5.18 **Downmix.......................................................35
5.19 Clocking.............................................................36
5.20 Word Clock In and Out......................................37
5.21 Error Messages..................................................38
5.21.1 ACU Over Temperature............................38
5.21.2 PSU Error..................................................39
5.21.3 Communication Error...............................39
5.21.4 Cooling Fan Error.....................................40
6 System Setup..........................................................40
6.1 Introduction.........................................................40
6.2 Workflow Setup...................................................42
6.2.1 Workflow Setup Main Screen.....................42
6.2.2 Select Workflow To Edit Screen.................43
6.2.3 Editing Workflow Screen............................44
6.2.4 Workflow Channel Setup Screen................45
6.2.5 Editing Workflow Rename Screen..............46
6.2.6 Editing Workflow Save and Exit................47
6.2.7 Editing Workflow Cancel............................48
6.2.8 Workflow Load...........................................49
6.2.9 Workflow Copy...........................................50
6.2.10 Workflow New..........................................51
6.2.11 Workflow Import From USB....................52
6.2.12 Workflow export to USB..........................54
6.2.13 Workflow delete........................................57
6.3 Setup....................................................................58
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m908 Preliminary User Manual, Rev. 04
6.3.1 Navigating and Using the Setup Menus.....58
6.3.2 Standard Parameter Editing........................60
6.3.3 Standard Name Editing...............................61
6.3.4 Standard Channel Routing..........................63
6.3.5 Input Setup..................................................65
6.3.6 Dim setup....................................................67
6.3.7 CR1, CR2, CR3 Speaker setup...................68
6.3.8 Bass Management setup..............................71
6.3.9 **SOLO/MUTE Setup................................71
6.3.10 Room Correction setup.............................73
6.3.11 Monitor Control setup...............................74
6.3.12 MONO setup.............................................76
6.3.13 (L-R) setup................................................76
6.3.14 CUE setup.................................................77
6.3.15 MUTE setup..............................................79
6.3.16 User A B C Switches Setup.......................80
6.3.17 Downmix setup.........................................81
6.3.18 Monitor Snapshot setup............................81
6.3.19 Meter Output setup....................................82
6.3.20 Talkback setup...........................................84
6.3.21 SPL Meter setup........................................86
6.3.22 Clock Source Setup...................................87
6.3.23 Word Clock Termination Setup.................88
6.3.24 Word Clock Output Setup.........................88
6.3.25 *GPIO Setup.............................................88
6.3.26 System Setup.............................................91
7 Option Modules......................................................93
7.1 ADC Option Module...........................................93
7.2 Dante Option Module..........................................94
7.3 DigiLink Option Module.....................................94
7.4 Phono Preamp Option Module............................95
8 USB Audio Setup...................................................96
8.1 Computer Audio Requirements...........................96
8.2 Windows USB ASIO Driver................................97
8.2.1 Installing USB ADIO Driver......................97
8.2.2 Using The USB ASIO Driver.....................99
9 **Firmware Upgrades..........................................101
9.1.1 Firmware Update Procedure.....................102
10 Electrical Specifications.....................................102
11 Block Diagrams..................................................102
12 Cable and Connector Diagrams..........................103
13 Dimensions.........................................................106
14 Warranty Information.........................................107
15 Illustrations Index...............................................108
16 Manual Revision History....................................109
List of Tables
Clock Status...............................................................36
Speaker Names...........................................................42
Workflow Templates..................................................48
GPIO FUNCTIONS...................................................79
GPIO VOLTAGE CONFIGURATION.......................81
Page 3 of 108 Table Of Contents
Dante Channel Count.................................................85
DB25 Digital AES3 (Tascam Pinout).........................92
DB25 Analog (Tascam Pinout)...................................92
DB15 RCU Connector................................................93
Manual Revision History............................................98
m908 Preliminary User Manual, Rev. 04
1 Welcome
Thanks for purchasing the m908 multi-channel monitor controller. It has been painstakingly
designed and built to provide you with a beautiful sounding, configurable and reliable monitoring
system. Please familiarize yourself with the setup and operational details contained in this
manual. And as always with this or any other Grace Design products, please don't hesitate to
reach out if you have any questions. We are available by telephone Monday – Friday, 9AM to
5PM MST, or by email at info@gracedesign.com. Also, other information including technical
documents and firmware can always be found on our website – www.gracedesign.com. Thanks
for reading and enjoy your m908!
2 Important Safety Information
2.1 General
• Indoor use only
• Ordinary Protection: This equipment should not be exposed to dripping or splashing.
• Avoid placing objects filled with liquids, such as vases or glasses, on this equipment.
• Class I Equipment (grounded type)
• Electrical rating: 90-240V~ 50-60Hz 40W
• Mains supply voltage fluctuations are not to exceed ±10% of the nominal supply voltage.
• Pollution Degree 2
• Installation (Over voltage) Category II for transient overvoltages.
• Maximum Relative Humidity: <80%
• Operation temperature range: 10 °C to 40 °C
• Storage and transportation temperature range –40 °C to 70 °C
• Maximum altitude: 3000m (9843 ft)
• Equipment suitable for continuous operation
2.2 Safety Marking Symbols
This symbol, located on the equipment and in this manual, refers to important instructions.
Read this manual thoroughly before operating this equipment.
This symbol, located on the equipment and in this manual, indicates the potential for
electrical shock hazard.
2.3 Service Information
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m908 Preliminary User Manual, Rev. 04
The Grace Design m908 contains no user serviceable components. Contact Grace Design for
repair and upgrade information. In the event that your Grace Design m908 needs to be returned to
the factory, contact us for a return authorization number.
2.4 California Proposition 65 Warning
This product may contain metallic nickel, a chemical known to the State of California to cause
cancer and birth defects or other reproductive harm. Wash hands after handling.
3 Overview And Features
3.1 Features
• 24 Channel DSP for immersive surround formats such as ATMOS™, DTS:X™ and Auro 3D™
• Manage playback systems from mono through 22.2
• Our latest generation of AD and DA converters
• Powerful and ergonomic remote control unit for access to all system controls
• 4th generation s-Lock pll clocking system for vanishingly low jitter
• High resolution volume control
• Up to 1 second sync delay
• Room correction EQ
• Full bass management
• Speaker channel level and delay calibration
• Comprehensive downmix control
• 16 channel analog out / 24 channel AES3 digital I/O
• 16 channel ADAT Lightpipe In / USB 24 channel In
• AES3, S/PDIF, and TOSLINK Stereo In
• Optional Dante™, DigiLink™ or MADI module for additional 32 channel I/O
• Optional 8 channel ADC module for 8 or 16 channel analog inputs
• Optional high performance RIAA phono preamplifier for MC and MM cartridges.
• Flexible Meter outputs
• Built in SPL meter
• Dual redundant external power supply
• Reference quality headphone amplifier with cross-feed.
• Flexible talkback system with built-in mic on remote control and mic input for external talkback
mics
• Up to 8 stereo CUE paths
• 4 General Purpose Input and Output pins for interfacing to external systems.
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m908 Preliminary User Manual, Rev. 04
The m908 consists of three components: ACU (Audio Control Unit), RCU (Remote Control Unit), and
PSU (Power Supply Unit) Below is a description of the connections, controls, and indicators for each
component.
3.2 ACU Description
The 2U ACU chassis houses all of the analog and digital audio IO, DSP processing, and
control IO. The audio signal processor is a 1GHz 32 bit floating point unit which allows for
highly accurate and low latency signal processing. 2GB of DDR2 ram allows for ample sync
delay across 24 channels at sample rates up to 192kHz. Audio routing, AES and ADAT encoding
and decoding is handled by an Artix-7 FPGA. The system is managed by an ARM Cortex-A15
processor running embedded Linux.
The m908 system clock is based on our 4th generation s-Lock PLL technology. This is an
incredibly low jitter PLL that provides exceptional ADC and DAC sample clocking accuracy.
The Audio and Clock flow is shown in the simplified block diagram below.
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AUDIO INPUTS
ROUTING
DSP
ADC OPTION
ANALOG 16CH
ANALOG 2CH
AUDIO OUTPUTS
DAC
ANALOG 16CH
HP AMP
RCU
DIGITAL OUTPUTS
AES DIGITAL 24CH
USB 8CH
DANTE 32CH
CLOCK
s-Lock PLL
WORD CLOCK I/O
IN OUT
ACU TALKBACK
RCU TALKBACK
DIGITAL INPUTS
AES DIGITAL 24CH
USB 24CH
ADAT 16CH
(TOSLINK 2CH)
DANTE 32CH
SPDF 2CH
AES 2CH
TALKBACK OUT
Illustration 1: Audio and Clock Flow Diagram
The audio signal processing signal flow is shown in the diagram below.
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1 2
AUDIO
INPUTS
INPUT SELECT
AND SUMMING
SPEAKER
DELAY
LEVEL
OFFSET
SPEAKER
LEVEL
OFFSET
Illustration 2: audio path flow diagram
3.3 ACU Front Panel Connections and Controls
SYNC
DELAY
SPEAKER
VOLUME
BASS
MANAGEMENT
AUDIO
OUTPUTS
Illustration 3: ACU Front Panel
1. 1/4" Headphone Jack: The m908 headphone amplifier is an ultra high performance current
feedback design. Very low output impedance ensures good damping factor at the headphone
driver. The proprietary crossfeed circuit provides natural imaging and minimizes listening
fatigue.
2. Power indicator LED: Green LED illuminates solid green under normal conditions. Flashing
indicates a fault contrition in the redundant power supply unit.
3.4 ACU Rear Panel Connections
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m908 Preliminary User Manual, Rev. 04
1 2
1
2
3
5
86
DC IN
A140-M908
PSU ONLY
TALKBACK SWITCH
ETHERNET
10 11
5 6 7 8 9
3 4
ADC 2
A
E
S
3
3
I
N
/
O
U
T
1
4
A
E
S
3
2
I
N
/
O
U
1
T
m908 RCU
A
E
S
3
1
I
N
/
O
U
T
1
1
4
1
9
m908 REFERENCE MONITOR CONTROLLER
1
1
4
HOST
AES3 IN
OPTION I/O
S/PDIF
OPTICAL IN AUDIO
WC OUT
2
1
WC IN
12 13 14 15 16 17 18 19
A908
ADC
A
N
A
L
O
G
I
N
1
-
8
1
4
A908
ADC
A
N
A
L
O
G
I
N
1
-
8
1
1
1
4
ADC
1
L
R
UNBAL IN
BAL IN
L L
R CR 3 OUT R
TB INTB OUT
MADE IN LYONS, CO USA
CR 1 OUT CR 2 OUT
1
14
- 8
(1
)
- 8
(1
) (
1
14
CUE/CR EXT.
9 - 16
)
1
14
20 21 22
Illustration 4: ACU Rear Panel
1. DC power input connector 8 Pin Circular: Connect to PSU. CAUTION: CONNECT PSU TO
ACU WITH DC POWER CABLE BEFORE APPLYING POWER.
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2. AES3 I/O x 3 DB25 (Tascam pinout) 110Ω: 24 channel input and output. Accepts sample rates
from 44.1kHz-192kHz.
3. Option I/O slot (Dante , Digilink, and MADI options): The Option I/O module can receive and
transmit 24 channels of PCM audio.
4. Analog balanced input ADC (optional): There are slots for two optional 8 channel ADC
modules with DB25 input connectors. The ADC modules plug in to the main digital pcb. Two
ADC modules can be used for a total of 16 channels. The ADC in position 1 is also connected
to the stereo balanced XLR and unbalanced phono jacks so that it can be used for monitoring
stereo sources on channels 1-2. Note that when monitoring the stereo connections, channels 1-2
on the DB25 connector are not heard.
5. Stereo Input analog unbalanced RCA Phono: Present if an ADC option module is installed. Can
be switched to Phono level if the RIAA Phonograph Preamplifier module is installed.
6. Stereo Input balanced analog XLR: Present if an ADC option module is installed.
7. Control Room 3 Output balanced analog XLR: Analog output signals sourced from DAC
channels 1-2.
8. Talkback output balanced analog XLR: Talback signal sourced from ACU or RCU Mic. Can be
configured to be momentary while talkback is active or continuously on.
9. Talkback mic input balanced XLR: Balanced microphone level input with available 48V
phantom power. The talkback signal is fed to an ADC and sent to the DSP section and also sent
to the Talkback output XLR connector. This is a full featured high performance microphone
preamplifier that can be used for recording and voice over applications.
10. External Talkback switch jack 1/4" TRS: Wiring a normally open switch to this jack will allow
for another talkback control. The Ring of this connector carries current limited 5V for
powering a tally LED. See Cable Diagrams.
11. Ethernet Control Port RJ45: Reserved for future use.
12. RCU serial control DB15: Connect to RCU with supplied DB15 cable.
13. USB Host USB-A: USB host connector for system firmware update.
14. AES3 Input XLR: Stereo AES digital input. Supports sample rates from
15. SPDIF Input RCA Phono
16. ADAT/TOSLINK x 2 Optical: Optical receivers for ADAT or TOSLINK. Supports SMUX for
8ch 96kHz operation.
17. USB Audio I/O USB-B: The USB Audio Class 2 compliant interface allows for monitoring up
to 24 channels of PCM audio at 48kHz/24bit and 8 channels of PCM audio at 192kHz/24bit.
18. Word Clock IN BNC 75Ω or 47kΩ (setup menu selected): External clock input.
19. Word Clock OUT / THROUGH BNC 75Ω: Output clock signal can be a buffered copy of the
incoming word clock or can be from the internal word clock.
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20. Control Room 1 output balanced analog DB25 (Tascam pinout): Analog output signals sourced
from DAC channels 1-8.
21. Control Room 2 output balanced analog DB25 (Tascam pinout): Analog output signals sourced
from DAC channels 1-8
22. CUE/WIDE OUT balanced analog DB25 (Tascam pinout): Analog output signals sourced from
DAC channels 9-16. These outputs can be for speakers in immersive playback systems or for
CUE outputs. CUE outputs have level control, assignable talkback summing, and MON>CUE
routing. MON>CUE sends the Left and Right signal from the current monitor signal to the
CUE output. In the case of multi-channel monitoring the Left and Right signal or a stereo
downmix can be sent to the CUE output.
3.5 RCU Description
The Remote Control Unit is designed to be a seamless interface between the user and the
audio system being controlled. We have carefully selected the display, switches, and encoder to
be long life and provide excellent tactile feedback. All of the necessary information is displayed
on the 1/4WVGA display while the most used functions have dedicated switches. There is a 1/4"
headphone jack on the rear of the RCU for convenient access to the m908s high performance
headphone amplifier.
The RCU sits on a tilting base so it can be adjusted to the most comfortable angle. The built in
talkback microphone on the RCU also doubles as an accurate sound pressure level (SPL) meter.
The RCU is powered from the ACU via the DB15 cable.
3.6 RCU Front Panel Controls
Many of the most used monitoring functions are directly accessed through the push button
switches on the RCU front panel. Primary functions are accessed with a press-release. Where a
switch has more than one function the primary function is indicated with large upper case letters.
The secondary function is indicated in small letters and is accessed with a push-hold of the
switch. Some switches can have secondary functions assigned to them by the user. These
switches do not have lower case labeling.
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TALKBACK
VOLUME
push for phones
MUTE
SETUPMON > CUE
CR 2 CR 3
MONO
x-feed
DIM
spl clear
L - R
L C R
RSLS
SUB
RB
SOLO/MUTE
A
LB
B C
CR
1
21 3 4 7 8 9
10111213
5 6
14
Illustration 5: RCU Front Panel
1. LCD Display screen: This color LCD displays all operating parameters and setup menus.
2. INPUT Select switches (8x): These switches select the input source to be monitored. See Input
Select operation for details.
3. DIM (x-feed): Dims the monitor system by a pre-programmed level. Push-hold enables/disables
the headphone cross-feed circuit. See DIM operation for details.
4. MUTE: Mutes the monitor system. See MUTE operation for details.
5. MONO (L-R): Sums the Left and Right channels (L+R). Push-hold for difference (L-R). See
MONO operation for details.
6. CR1, CR2, CR3: Control Room Speaker system select. See CR1 CR2 CR3 operation for details.
7. MON > CUE (spl clear): Sends the current source being monitored to the CUE sends. Pushhold clears the maximum spl field in the sound pressure level meter. See MON>CUE operation
for details.
8. SETUP: System Setup access. Push-Hold for System Workflow setup. See System Setup and
Workflow Setup for details.
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m908 Preliminary User Manual, Rev. 04
m908
ACU
1 2 3 4
9. L, C, R, LS, SUB, LR, LB, RB: Speaker select for SOLO or MUTE. See SOLO MUTE for
details.
10. SOLO/MUTE: Selects between SOLO and MUTE monitoring mode. See SOLO MUTE for
details.
11. A, B, C: User programmable switches. See A B C User Switches operation for details.
12. VOLUME: Monitor level control for Control Room speakers and headphones. See VOLUME
operation for details.
13. TALKBACK: Talkback is activated by pushing this switch. See TALKBACK operation for
details.
14. INPUT Select switch and Input Page change. See Input Select operation for details.
3.7 RCU Rear Panel Connections
Illustration 6: RCU Rear Panel
1. m908 ACU DB15: Serial control cable connection to ACU
2. Headphone Jack 1/4" TRS: Carries stereo headphone signal from ACU headphone amplifiers.
This jack is wired in parallel with ACU front panel headphone jack.
3. USB Host USB-A: USB host connection for user configuration export/import and RCU
firmware update.
4. Microphone: Built in mic for talkback and spl measurement
3.8 RCU Tilting Base
The RCU features a tilting base so that it can be tilted to an angle for optimal viewing. Loosen
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A140 REDUNDANT DC POWER SUPPLY UINT
OK
PS #1 FAULT
PS #2 FAULT
CAUTIO N: CONNECT DC POWER CORD B EFORE T URNING ON PO WER
+18V
+6.5V +50V
-18V
1
2
the four thumbscrews located on each side of the RCU and tilt the unit to the desired angle.
While holding the RCU at this angle tighten the four thumbscrews. The tilt range is from
horizontal to 30º.
3.9 PSU Description
The m908 monitor controller is powered by the A140 Dual Redundant Power
Supply Unit. The A140 features Universal AC Input for operation from 100240VAC. This new generation external power supply contains two complete power
supply modules which operate in parallel. Should one power supply module fail
the other module will continue to power your system with no interruption. The A140 contains an
intelligent microprocessor that monitors all of the DC rail voltages and reports fault conditions by
flashing front panel LEDs. In the unlikely event that a power supply module fails the A140 front
panel LEDs with flash to indicate which power supply module is at fault. The power supply
modules are easily replaced in the field which minimizes any possible system down time.
A low speed serial communication link allows the power supply unit to communicate voltage
rail status to the main ACU processor.
Under normal operating conditions the four front panel Status LEDs will be solid green.
If a DC output of power supply module #1 becomes too low or too high the corresponding LED
will flash once repeatedly. If a DC output of power supply module #2 becomes too low or too
high then the corresponding LED will flash twice repeatedly. If this happens contact Grace
Design Technical Support at 303-823-8100 x105 or service@gracedesign.com
3.10 PSU Front Panel Controls and Indicators
Illustration 7: PSU Front Panel
1. Voltage rail monitor LED x 4: These LEDs will illuminate steady green under normal operation.
2. Mains power switch: This is the AC Mains disconnect device. It must remain accessible.
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m908 Preliminary User Manual, Rev. 04
A140-m801
A140-m802
A140-m906
A140-m908
MADE IN USA
100-240VAC
50W MAX
2 31
3.11 PSU Rear Panel Connections
Illustration 8: PSU Rear Panel
1. Fuse drawer: Contains (2) 5x20mm 800mA Time Delay fuse.
2. AC Power inlet: 90-240V~ 40W max. Connect to a grounded outlet.
3. DC Output connector: ALWAYS connect DC power cable to m908 before turning on power and
turn off the power before disconnecting the DC power cable!
4 Installation
4.1 Unboxing your m908
4.1.1 Open and inspect your box
Please take care when removing the m908 from its OEM packaging. Our packaging is
designed with ‘Korrvu©’ suspension inserts, which provide the best protection from the dubious
underworld of freight handling – so save your packaging material. Inner boxes will contain all
the items listed below. If you think you are missing anything, give your dealer or us a call and
we’ll get you taken care of right away.
4.1.2 Your box will contain
• 1pc Audio Control Unit (ACU)
• 1pc Remote Control Unit (RCU)
• 1pc Power Supply Unit (PSU)
• 1pc AC power cord
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m908 Preliminary User Manual, Rev. 04
• 1pc DC power cord 8’ (2.8m) (Grace Part No. WA084)
• 1pc DB15 Remote Cable, 25' (7.6m) (Grace Part No. WA141)
• 1pc USB 2.0 Cable, Type A to Type B, 6 foot (Grace Part No. WA551)
• 2pc spare fuses. 800mA 250V~ Time Delay 5x20mm (Grace Part No. F101, Littlefuse
0239.800HXP or equivalent)
• 4pc Adhesive backed rubber feet, 0.12" thick (Grace Part No. H560)
• 4pc Adhesive backed rubber feet, 0.23" thick (Grace Part No. H580)
• 4pc 10-32 X 3/4 Truss Head Phillips rack mount screw (Grace Part No. H455)
• 1pc m908 User Manual
4.1.3 REGISTER YOUR UNIT
We strongly urge you to fill out your warranty registration card. The m908 is covered by a 5
year transferable warranty. Registering your unit will help us contact you if there are important
updates and simplifies warranty service. So please take a few minutes to complete and send in the
enclosed card, or simply fill out the warranty registration form on our website. We always keep
your information private. Thank you!
4.2 Connecting the m908
4.2.1 Power Connections
A DC power cord is supplied to connect the PSU to the ACU. This cord can be
identified by the 8 pin circular connectors at each end.
Please note that the DC power cord should be connected before the AC power is turned
on. This prevents incorrect power sequencing which can cause damage to the audio circuits. To
avoid any interference with the low level audio circuitry, the power supply should be located at
least 3’ (1m) from the ACU.
WARNING: A damaged DC power cord can create a shock hazard as voltages of 72VDC can
be present.
Do not operate the m908 with a damaged DC power cord. If damage occurs, please contact
Grace Design for a replacement. A standard AC power cable is included. For safety, the power
supply cord must be connected to a grounded outlet.
4.2.2 Audio Connections
Talkback Microphone Input: Female XLR, pin 2 positive, pin 3 negative and pin 1 ground.
48V phantom power is supplied on pins 2 and 3. With a gain range +7dB and +15-70dB in 1dB
steps this inputs can be used for any type of microphone or as a line level input.
Talkback Microphone Output: Male XLR, balanced, pin 2 positive, pin 3 negative and pin 1
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ground. Provides a direct output of the talkback microphone preamp.
Analog Balanced Control Room Outputs: DB25 Tascam pinout (See CABLE
DIAGRAMS). These outputs are defined in the setup menus for your control room speaker
system.
Analog Balanced CUE/WIDE Outputs: DB25 Tascam pinout (See CABLE DIAGRAMS).
Depending on your workflow these outputs are defined in the setup menus for your additional
surround/overhead speakers or CUE outputs.
Analog Balanced Stereo Control Room Output: Male XLR, balanced, pin 2 positive, pin 3
negative and pin 1 ground. These outputs are defined in the setup menus for your control room
speaker system.
AES3 Digital I/O: DB25 Tascam pinout, 110Ω (See CABLE DIAGRAMS)
ADAT Lightpipe / TOSLINK Inputs: In ADAT Lightpipe Mode these optical jacks provide
8 channels of audio data on each (at 44.1kHz and 48kHz). With ADAT S-MUX enabled 88.2kHz
or 96kHz sample rate audio channels 1-4 are received on OPTICAL input 1, while channels 5-8
are received on OPTICAL input 2. 176.4kHz and 192kHz sample rates are not supported over the
ADAT interface. In TOSLINK mode stereo signals up to 96kHz can be received on each
connector. See the System Setup section of this manual for details on configuring the optical
input connectors.
SPDIF Digital Stereo Input: RCA Phono jack, 75Ω. This input will receive PCM audio
signal sample rates from 44.1kHz to 192kHz.
USB Class 2 Audio Interface: USB Type B jack. This interface is capable of 24 channel
input from host computer and 8 channel output to the host computer. Use a standard USB type A
-to- type B cable (included with your m908). The type A connector is to be plugged in to the
HOST computer and the type B connector to the m908 input. PCM 44.1kHz – 192kHz/24 bit is
supported. Please refer to USB Audio Setup.
4.2.3 Optional ADC Module Connections
Analog Balanced 8 Channel Line Inputs: DB25 Tascam Pinout (see CABLE DIAGRAMS).
8 channel ADC module balanced inputs. Internal jumpers select input sensitivity of
+18dBu=0dBFS or +22dBu=0dBFS.
Analog Balanced Stereo Line Input: Female XLR, balanced, pin 2 positive, pin 3 negative
and pin 1 ground. Supplied with ADC Option Module. Allows for the connection of balanced
stereo sources to the ADC. Left channel is connected to ADC 1 channel 1 and Right channel is
connected to ADC 1 channel 2.
Analog Unbalanced Stereo Line Input: RCA Phono. Supplied with ADC Option Module.
Allows for the connection of unbalanced stereo sources to the ADC. Left channel is connected to
ADC 1 channel 1 and Right channel is connected to ADC 1 channel 2.
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4.2.4 Clock and Control Connections
REMOTE CONNECTOR: DB15 The m908 RCU handles all system control. Connection to
the m908 RCU is via this DB15 connector, which carries RS485 serial data, DC power and
headphone signals. The m908 ships with a high quality 25’ cable. Custom cables can be
assembled by the user according to the diagrams in the Cable Diagram section of this manual.
While the serial data can travel over 1000 feet we do not recommend cables longer than 50’ for
headphone use. If you need a longer, cable contact your Grace Design dealer or us directly. Do
NOT use an off the shelf DB15 cable as the pinout will be incompatible and may cause damage
to your system.
WORD CLOCK IN: BNC 75Ω or 47kΩ (setup menu selected). The m908 can accept a
standard 5V/75Ω word clock signal from an external clock generating unit. This might be a
stand-alone clock source or via, for example, the word clock output from your digital audio
workstation. The m908 locks to the incoming word clock with an ultra low jitter PLL. The PLL
has a fast lock mode which rapidly acquires lock and then switches to a high jitter rejection mode
with a loop bandwidth of 0.5Hz. This provides exceptional jitter rejection for the DAC and ADC
sample clocks. In the event of a dropout or loss of incoming word clock signal, the intelligent
PLL will remain at the last known valid frequency. When the signal is restored the PLL will
smoothly re-acquire lock.
WORD CLOCK OUT: BNC 75Ω. The word clock output allows the user to synchronize
other digital audio equipment to the m908. When the system menu setting "clock output" is set to
external, this connector output is a buffered copy of the signal on the word clock IN jack. This
mode is useful for "daisy chaining" to other units in a system. When "clock output" is set to
system clock this connector outputs a buffered copy of the internal m908 word clock. The output
is buffered and is designed to drive a 75Ω line.
ETHERNET: RJ45. This is a standard 1000 Base-T Ethernet interface. Currently it is
reserved for factory diagnostics.
USB HOST: USB A connector. This host connector is intended for firmware upgrades.
EXT. TALKBACK: 1/4" TRS Jack. External talkback control. This input allows the
connection of an external switch, such as a footswitch, for remotely activating the ACU talkback
mic input, or the built in talkback mic on the RCU. The input is a TRS jack and is used with a
“normally open” switching device. Note that when using this jack the talkback function can be
activated at both the RCU and the remote switch. See the remote talkback cable diagram at the
end of this manual for connection details.
4.2.5 Thermal Management
The m908 ACU requires adequate ventilation to maintain proper operating temperature.
Under normal operating conditions the m908 will dissipate 30-35W of power depending on
user settings. To protect the m908 from excessively high internal temperatures, and to ensure
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long term reliability, it is equipped with a 40mm variable speed fan. Whether or not this fan turns
on is dependent on several variables. These are: ambient temperature, whether there is air
movement around the m908, and if the m908 is mounted directly above or below other heat
generating equipment.
The variable speed fan to comes on to cool the internal circuits if the main circuit board
temperature rises above 45ºC (113ºF). The fan has four speed ranges which are triggered by the
following pcb temperature thresholds:
1. Low: 45ºC (113ºF)
2. Med: 49ºC (120ºF)
3. High: 52ºC (125ºF)
4. Max: 55ºC (131ºF)
If the m908 is mounted without space above and below and it is adjacent to heat generating
devices then the internal temperature can rise above 45ºC and the fan will come on.
If the m908 is being used in an area where fan noise is undesirable it is recommended that the
m908 be mounted such that it has space below and above the chassis and where the ambient
temperature does not exceed 30ºC (86ºF).
5 Operation
Out of the box the m908 comes with a many factory presets that will allow for quickly
connecting the most common input sources, cue, and speaker systems. If your installation
requires customization, then see the Workflow Setup and Setup sections of this manual.
Otherwise read this section for the basics on operating the m908.
The m908 uses a closed loop control system to ensure that the status reported on the RCU
matches the actual hardware setting in the ACU. Any changes made to the configuration of the
system are transmitted to the ACU, where they are processed and reported back to the RCU for
confirmation. The following sections detail all of the controls and features of the normal
operation mode.
5.1 Manual conventions
Throughout the Operation and Setup sections of this manual references to screen elements and
setup menu parameters will use the following formatting:
• Hardware controls and connectors will be in ALL CAPITOL LETTERS
• Switches with secondary functions will be (in parentheses)
• Setup menu screen names will have the First Letter capitalized
• Setup parameter names will be in bold lower case
• Setup parameter values will be <enclosed>
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• "push" refers to a quick push and release of a switch.
1
2
3
4
5
8 7
6
9
• "push-hold" refers to a 1/2 second push and hold of a switch.
• "push long-hold" refers to a 3 second push and hold of a switch.
5.2 Home Screen
m908 Preliminary User Manual, Rev. 04
Illustration 9: Home Screen
The home screen provides an overview of the m908 system status.
5.2.1 1 Input Selection
The top and bottom bands of the LCD display area show the input sources available for
monitoring. The currently selected input will be highlighted in blue. With Input Summing Mode
active, the selected input(s) will be highlighted in green.
5.2.2 2 Control Room Speakers Layout Icons
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The Control Room speaker system layout window displays a graphic representation of the
currently selected speaker system. There are 4 types of speaker icons.
1. Front and Surround
m908 Preliminary User Manual, Rev. 04
2. Top
3. SUB
4. Height
Each icon also acts as a signal level indicator. The level is monitored post-processing
and pre-volume control.
• White No signal present.
• Green Signal greater than -50dBFS
• Yellow Signal greater than -6dBFS
• Red Signal OVER
In the lower center area of the speaker system layout window is the solo/mute page and status.
The word "solo" will be visible in gray when the system is in solo mode. The word solo will be
visible in white when there is a speaker in solo mode.
The word "mute" will be visible in gray when the system is in mute mode. The word "mute"
will be visible in white when there is one or more speaker in mute mode.
The speaker system can be configured in the Speaker Output setup
5.2.3 3 Control Room Speaker Output
The name of the currently selected Control Room speaker system is displayed directly above
the Control Room Monitor Level.
5.2.4 4 Control Room Monitor Level
The current control room monitor level is displayed in large numbers which will be green
when the encoder is controlling the control room level. The default volume range is 0-100 in
0.5dB steps. 0 is mute and 100 is unity gain.
The Control Room Monitor Level can also be displayed with a user defined reference level.
This way the volume readout can be calibrated to SPL.
See Monitor Control setup for details on configuring the Control Room Monitor Level display.
5.2.5 5 Headphone Crossfeed
The Headphone Crossfeed circuit status is displayed in the upper right corner of the
headphones volume display window. See the X-FEED section of this manual for details.
5.2.6 6 Headphone Monitor Level
The current headphone monitor level is displayed in small numbers which will be green when
the encoder is controlling the headphone level.
See Monitor Control setup for details on configuring the Headphone Monitor Level display.
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5.2.7 7 SPL Meter
Using the internal m908 RCU microphone, the m908 computes the real-time sound pressure
level based on the system configuration. The current and peak SPL levels are displayed along
with the filter mode in this section of the display. The peak spl value can be cleared at any time
with a push-hold of the MON>CUE (spl-clear) switch. The SPL measurement settings are
configured in SPL Meter setup.
When talkback is activated on the RCU, SPL monitoring will be suspended and the built in
microphone will switch to become the talback mic. The SPL Display area will indicate
TALKBACK ACTIVE. Upon exiting Talkback the SPL meter will return to normal operation.
5.2.8 8 Clock Source and Status
The clock status window displays the current clock source and indicates it's status by changing
the color of the text. See the Clocking section of this manual for details.
5.2.9 9 System Sample Rate
The sample rate display indicates the sample rate detected on the input connector. If the input
data or sample rate is invalid then the sample rate display will be blank (--).
5.3 INPUT SELECT
The m908 features a total of 16 input sources which are accessed with 8 dedicated INPUT
Select switches, in 2 rows of 4, above and below the LCD display. Each INPUT Select switch is
located adjacent to it's name area in the upper and lower bands of the display area. Pushing any of
these switches will select the associated input source and connect it to the monitoring path. When
an input is selected for monitoring it's name area background will be blue. Inactive inputs will
have a gray background in the name area.
The 16 inputs are displayed across two "pages" of 8 inputs. To switch between the input pages
push-hold the lower right INPUT select switch. The input name area next to the lower right hand
INPUT switch will show which page is currently being displayed with two small dots. When the
left dot is white inputs 1-8 are displayed. When the right dot is white inputs 9-16 are displayed.
Illustration 10: Input Page Select
Each input can be custom defined in the Setup Menu. The hardware connector, channel count,
level offset, sync delay, clock override mode, and name can be configured. See the Input Setup
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section of this manual for details.
5.3.1 Input Summing Mode
The m908 allows up to three inputs to be summed. To enter summing mode, simultaneously
press the INPUT select switches for up to three of the desired inputs to sum. The inputs will
become active at the same time and the name areas will turn green on the display.
To change the inputs that are being summed press the INPUT select switches for the channels
that are to be removed from the sum then press the INPUT select switches for the channels that
are to be added to the sum.
Pressing any of the active INPUT select switches will toggle that input on and off in the sum.
To exit input summing mode simply de-select the inputs that you don't want in the sum. When
only one input is active push that switch and summing mode will turn off. The input name area
will be displayed in blue.
Any input that has clock override enabled can not be summed with other inputs.
Inputs that do not have identical Input sync delay settings can not be summed together. This is
because the delay happens after the input summing section in the m908.
Note: If the Meter Outputs are to provide metering for summed input signals the meter output
source must be set for <follow monitor post>.
5.4 DIM
The multi-function DIM / (x-feed) switch controls the monitor DIM and headphone x-feed
features.
Speaker DIM attenuates the current control room speaker system and/or the headphones by
the preset attenuation level. When dim is active, the switch is lit solid yellow.
DIM level and which outputs it affects can be configured in Dim setup.
5.5 X-FEED
Press-hold of the DIM / (x-feed) switch engages the Headphone cross-feed circuit in the
headphone output. When x-feed is active it is indicated on the headphone status display. X-feed
(cross-feed) simulates the acoustics of a loudspeaker listening environment which can
significantly improve imaging while reducing listening fatigue when using headphones. This
feature employs carefully designed signal cross-feed, filtering and delay circuits to simulate hrtf
(head related transfer functions).
Press-hold the DIM (x-feed) switch to toggle Headphone Crossfeed on and off. Crossfeed is
indicated in the upper right corner the phones volume window.
When listening to loudspeakers in a room, your left ear hears sound primarily from the left
speaker (and vice versa) but also receives a signal from the right speaker at a lower level and with
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some time delay compared to the right ear. As well, the right speaker sound that reaches the left
ear does not have a flat frequency response as the sound waves have traveled around the shape of
your head before reaching your left ear. The brain uses delay, level and frequency response
characteristics to process the location of a sound and hence, create an aural image.
When listening to a stereo (or down-mixed) signal through headphones, each ear only hears
the sound from one transducer and the mixing of signals between the ears does not exist. In this
situation the brain is left without many of the psycho acoustic clues required to generate a
properly distributed image and an accurate sound stage. The result is that sounds seem to cluster
in the far left, far right or center of your head. Since the vital clues are absent, the brain has a
difficult time deciding how to process the sounds coming from the headphone, which can result
in listening fatigue when listening for extended periods of time. The m908 contains circuitry
which electronically simulates the signal cross-feed that occurs in a real acoustic space and helps
the brain establish instrument locations across the entire sound stage. While it is difficult to
perfectly model the very complex level, delay and frequency response characteristics of the head,
the cross-feed circuitry in the m908 gives the brain some of the basic clues it needs and the result
is a very pleasing simulation of an acoustic space. We chose the parameters of the cross-feed
circuit to find a good compromise between accurate imaging and tonal neutrality. For recreational
listening there could be more aggressive modeling of the head related transfer function (HRTF)
but this is usually at the expense of adding tone color. For critical monitoring during the
recording/editing/mixing process the user will find that the m908 cross-feed circuit provides a
sonically neutral character.
Below is a flow diagram and frequency response plot showing the response of the m908
crossfeed circuit. In this graph one channel of the headphone amplifier is driven. The two traces
show the direct channel and the opposite (cross-feed) channel.
Illustration 11: Headphone Crossfeed Flow Diagram
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+5
+0
-5
-10
-15
-20
-25
dB
-30
-35
-40
-45
-50
-55
20 50k50 100 200 500 1k 2k 5k 10k 20k
Hz
DIRECT SIGNAL
CROSSFEED SIGNAL
Illustration 12: Headphone Crossfeed Response Plot
5.6 MONO / (L-R)
The multi-function MONO / (L-R) switch controls the MONO and the L-R (Left minus Right)
features.
Pressing the MONO causes the output of the m908 to play in mono.
When speaker / headphone MONO is active, the switch is lit solid yellow.
Press-hold of the MONO switch enters L-R mode. In this mode the m908 subtracts the right
channel from the left channel and provides this signal to the monitor output.
When L-R is active, the switch flashes yellow.
Press and release MONO witch:
• Toggles mono on and off. Disables L-R if currently active.
Push-hold switch:
• Toggles the L- R mode on and off. Disables MONO if currently active.
The MONO and L-R processing can be applied to the Control Room speakers and/or the
headphone outputs.
The signal source for the MONO and L-R processing can be the Left and Right channels of
whatever input is being monitored. The output of the MONO and L-R processing can be the Left
and Right speakers or the Center speaker.
See the MONO setup and (L-R) setup for configuration options.
5.7 MON>CUE
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The MON>CUE switch activates Monitor to Cue mode which routes the currently selected
monitor source to the CUE outputs. The MON>CUE function can be enabled or disabled for each
of the cue outputs. Also, the send to the cue outputs can be the Left and Right channels of the
current monitor source or a stereo downmix if the source is in surround.
When active the MON>CUE switch will illuminate green.
See the CUE setup for configuration options.
5.8 MUTE
The MUTE switch mutes the audio in the control room speaker and/or the headphones. When
active the MUTE switch will illuminate red.
See the MUTE setup for configuration options.
5.9 CR1, CR2, CR3
Speaker system selection is made with one of the three CR (Control Room) switches.
Each output is defined in the Setup Menu. The hardware connector, channel count, level
offset, delay, bass management parameters, room correction eq, and name can be configured in
the CR Setup section of this manual.
The control room speaker select switches are exclusive and only one can be selected at a time.
The currently selected speaker switch will illuminate green.
5.10 BASS MANAGEMENT
The m908 includes comprehensive Bass Management control. Each speaker in the Control
Room system can be individually configured for crossover frequency, high pass filter slope, and
low pass filter slope. The internal summing of the LPF signals is done in stereo. All left channel
speakers are added to the Left sub bus, right channel speakers are added to the Right sub bus, and
center speakers are added to both busses equally. The user can decide to use stereo sub woofers
or use a mono sum of the stereo bus.
The high pass filter can be bypasses to a full range signal is sent to the speaker. As well, the
low pass filter can be turned off so that no signal is sent to the sub woofers.
See the Bass Management setup section of this manual for details.
The LFE input channel contains a variable low pass filter and a 0 or +10dB gain setting. These
are system level settings which are contained in the Monitor Control setup. See the Monitor
Control setup section of this manual for details.
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IN 2,3...
IN 1
OFF
20-150Hz HPF
20-150Hz LPF
50-150Hz HPF
6,12,18,24dB/oct
50-150Hz LPF
6,12,18,24dB/oct
OUT 2, 3...
WORKFLOW
DEPENDENT
OFF
OUT 1
WORKFLOW
DEPENDENT
OFF
SUB MODE
IN LFE
80-120Hz LPF
0dB
+10dB
Σ
Σ
SUB OUT L
SUB OUT C
SUB OUT R
Σ
SUB MODE
Illustration 13: Bass Management Flow Diagram
5.11 ROOM CORRECTION
The Control Room speaker output channels each contain up to 6 fully parametric bands of
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equalization for correcting minor frequency response aberrations in your control room.
The first 7.1, 7.2 or 7.3 channels in a speaker system will have 6 bands of eq per speaker. The
remaining speaker channels (if any) have 3 bands.
Each band of eq can be set for high pass, low pass, high shelf, low shelf, and peak response.
See the Room Correction setup section of this manual for details.
5.12 TALKBACK
The m908 has a flexible talkback system that can be adapted to a wide range of applications.
There is a microphone built in to the RCU and a talkback mic amp built in to the ACU. The
talkback microphones can be controlled from multiple trigger sources and routed to multiple
CUE paths. Trigger sources include the RCU TALKBACK switch, an external talkback switch
jack on the ACU, A B and C User switches, and GPIO input pins. As well, GPIO pins can be
programmed to output a logic level tally when talkback is active. Multiple routing configurations
allow different talkback triggers to route talkback audio to various CUE sends. For instance, you
can have the main TALKBACK switch on the RCU send talkback audio to all cue sends while
USER A switch can send talkback audio to only a specific CUE output.
The analog XLR Talkback Output jack on the ACU outputs the talkback signal from the
currently active talkback mic. This allows the Talkback signal to be sent to other headphone
systems or studio playback speakers.
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CUE INPUT 1
CUE OUTPUT 1
CUE INPUT 2
CUE OUTPUT 2
RCU TALKBACK MIC
ACU TALKBACK MIC AMP
MON>CUE
MON>CUE
CR MONITOR INPUT
Σ
MON>CUE
CUE ASSIGN
TALKBACK SWITCH
CUE ASSIGN
TALKBACK SWITCH:
RCU, EXT, A-B-C,OR
GPIO
RCU TALKBACK MIC
SWITCH ASSIGN
TALKBACK SWITCH:
RCU, EXT, A-B-C,OR
GPIO
ACU TALKBACK MIC
SWITCH ASSIGN
TALKBACK SWITCH:
RCU, EXT, A-B-C,OR
GPIO
TALKBACK SWITCH
CUE ASSIGN
TALKBACK SWITCH:
RCU, EXT, A-B-C,OR
GPIO
Σ
ACU TALKBACK OUT
Illustration 14: Talkback-Cue Flow Diagram
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The TALKBACK, ABC, and external talkback switches use an automatic latch/momentary
operation. A quick press-release will latch the talback mic on. Press-release again to turn talkback
off. Pushing and holding the talkback switch will activate talkback only while the switch is being
held down (momentary mode).
Pressing and releasing these switches quickly latches the talkback function on or off. Pushhold of the TALKBACK switch operates the talkback function for as long as the switch is held
down.
See the Talkback setup section of this manual for configuration details
5.13 SOLO/MUTE
The nine bi-colored SOLO/MUTE switches are used to solo or mute any individual channel or
group of channels being monitored. Eight of the switches engage solo or mute for the relevant
channel, while the solo/mute switch is used to toggle between solo or mute mode.
When in Solo mode the SOLO/MUTE switch will illuminate green. Pressing any of the 8
SOLO/MUTE switches will toggle solo mode on and off for that channel. In the speaker layout
window the word "solo" will appear in green and channels that are not soloed will be grayed out.
When in Mute mode the SOLO/MUTE switch will illuminate red. Pushing and of the 8
SOLO/MUTE switches will toggle mute mode on and off for that channel. In the speaker layout
window the word "mute" will appear in red and channels that are muted will be grayed out.
The SOLO/MUTE switches handle a complete 7.1 speaker system. However, if your speaker
system has more than 8 channels the SOLO/MUTE switches can "page" to the higher order
channels.
To page to higher order channels push-hold the RB switch. To page to lower order channels
push-hold the LB swich. The current solo/mute page is indicated in the group of 3 small dots in
the middle area of the speaker layout section of the LCD display. The current solo or mute mode
is indicated right above the page dots.
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